1. Field of the Invention
The present invention relates to a safety glass and a prelaminate therefor, which are effective in affording protection against lacerative injuries at the time of collisions and which provide excellent penetration resistance as well as excellent heat resistance, water resistance and optical properties. More particularly, the present invention relates to a safety glass and a prelaminate therefor, which are most suitable for a safety glass for automotive windows.
2. Description of the Prior Art
Laminated glass prepared by laminating and heat-pressing a pair of glass sheets with a polyvinyl butyral layer (hereinafter referred to simply as a "PVB layer") interposed therebetween, has been widely employed for automotive windshields. As an improvement in the safety of such conventional laminated glass, particularly, in the protection against lacerative injuries at the time of collisions, a safety glass comprising a single glass sheet or laminated glass sheet and a plastic film of e.g. polyethylene terephthalate bonded t the interior side of the glass sheet by a PVB layer, is proposed in e.g. U.S. Pat. No. 3,900,673 or 4,469,743. Such a safety glass affords a merit such that since an antilacerative plastic film is provided on the interior side of the safety glass, even when the glass sheet has shattered, it is possible to reduce the danger of the shattered glass pieces injuring the body of the passenger. However, as a result of various tests, the following difficulties have been found. Namely, the safety glass wherein a plastic film is bonded to a glass sheet or laminated glass sheet by means of a PVB layer, has been found to have difficulties such that when it is subjected to a boiling test, foaming takes place in the PVB layer, and when a hard object is pushed against the plastic film surface, a dent is likely to form and remains as a permanent deformation, or that when it is heated, the plastic film surface tends to be uneven, and the optical properties deteriorate. Such difficulties are believed to be attributable to the poor water resistance of the PVB layer and the thermoplasticity of the PVB layer such that it starts to soften at a temperature of about 60.degree. C.